With the advancement of an aberration correction technology, a Transmission Electron Microscope (TEM) and a Scanning Transmission Electron Microscope (STEM), which include an optical image forming system, are utilized as a device for observation of a semiconductor integrated circuit. In image data, which is observed by such a device, noise is mixed due to various factors. Therefore, a noise removal process or a noise reduction process may be performed. Improvements in such noise removal/reduction processes remain desired.